264 GEOLOGY AND MINING INDUSTRY OF LEADVILLB. 



and which are more or less intimately connected with the faults. The 

 other seven sections (J to P) run north and south and give the effects of 

 lateral pressure. As these are more or less parallel to the fault planes, 

 they intersect the latter generally at an acute angle, and the angle of inter- 

 section is often much lower than the actual slope of the fault plane. 



In representing the slope of the fault planes, in all cases where there 

 were no data from actual developments it has been given as inclining toward 

 the hanging- wall side at an average angle of 75°, and when cut diagonally 

 by the plane of the section the angle of intersection was calculated from 

 these. premises. As all these sections are carefully constructed to scale and 

 have a common base line, which is taken at 9,000 feet above sea-level, they 

 represent with a high degree of accuracy the surface of the country and the 

 relative thickness of the different sedimentary bodies, and in less degree that 

 of the porjAyry bodies, as far as can be deduced from their surface outcrops. 

 In order to show as far as possible the data from which these sections 

 have been constructed, the various shafts on or in close proximity to the 

 plane of each have been indicated on the sections by lines running below 

 the surface to show the depth to which their explorations have reached, 

 full lines indicating those on the section plane, dotted lines those near it. 

 The relative frequency of these shafts is therefore an indication of the com- 

 parative accuracy of the different portions of the section. It must, how- 

 ever, be borne in mind that the underground structure has been arrived at 

 not solely by consideration of the shafts on the actual line of the section, 

 but also by the consideration of the data obtained from the exploration of 

 shafts over a comparatively large area, which afford grounds from which the 

 theoretical structure may be deduced. 



Section A. — Scctiou A runs along Prospect Mountain ridge a little 

 south of its crest and crosses diagonally the valley of the east fork of the 

 Arkansas near its mouth. Its line lies entirely north of the extreme limits 

 to which the movements of the faults have been traced. Its structure lines 

 contrast strongly with those of the other sections on account of the broad 

 and regular curves. This contrast is probably greater than that existing- 

 in nature from the fact that actual data from beneath the surface along this 

 line ai'e almost entirely wanting, and the underground outlines are simply 



